Los Derechos No Enunciados 27

Seabirds are adapted to situations where the food availability rarely falls below the limit required to the survival of the adults (Cairns 1992b). The major task of the parents during the chick rearing period is then to provide food to their chicks in short and regular intervals of time. Seabirds, particularly penguins, feed in a limited foraging zone during breeding which can cause a food depletion near the colony as the season

progresses (Ashmole 1971; Birt et al. 1987). Birds need to take advantage of the best time of the year to start to breed in order to provide high energy food at least during the first 6 weeks of the exponential growth of the chicks. They may prefer to feed on fish which have a higher energy content than cephalopods and krill (Gales and Pemberton 1990). All these factors impose temporal and geographic constrains on the seabird foraging behaviour and seabirds will respond differently to this limiting factor

according to the availability of food (Barrett 1992; Cairns 1992b). In Chapter 5 it was suggested that the food provisioning to the chicks of little penguins is partially a response to the growing chick. However, the diet composition related to the age of the chick did not contrast from the temporal changes in prey available to the parents. This agrees with Cullen et al. (1992) that the diet composition of little penguins reflects food availability and they are probably opportunistic rather than selective feeders.

Temporal sampling and chick age were not totally independent events since sampling started as soon as the first group of eggs hatched and fewer later breeders were sampled; and therefore the results may be biased towards the early breeders. This was the first time that the diet composition of little penguin chicks was examined and it was restricted to one breeding season. Future inter-seasonal research on little penguin diet, using breeders with chicks of known age needs to address whether the non-selective feeding behaviour is responsive between breeding seasons of different food availability.

7 General conclusion7

This study records aspects of the breeding biology and feeding ecology of the little penguin Eudyptula minor throughout 1995/96 and 1996/97 breeding seasons. This study was initiated as a first step to assess the little penguin as an indicator in a monitoring program that examines changes in the availability of prey in the marine ecosystem around Phillip Island. The approach taken was similar to that for monitoring Adélie penguins as part of the CCAMLR8 Ecosystem Monitoring Program (CEMP). Parameters related to the breeding biology and feeding ecology of the little penguin were selected based on the CEMP experience. These parameters were thought likely to reflect changes in the food supply available to the little penguins during the breeding period.

The 1995/96 breeding season was characterised by poor breeding success where only 0.3 chicks were fledged per breeding pair. This compares with a 20 year average of 0.8 chicks per pair (Dann and Cullen 1990). The 1996/97 breeding season by contrast had very good reproductive success producing 1.3 chicks per pair. The difference between these two seasons was attributed to availability of food within the normal foraging range of little penguins from Phillip Island. This attribution could only be inferred since it was not possible to obtain contemporaneous data on the distribution and abundance of prey items and only one full breeding season’s data (1996/97) on diet composition was collected. However given the variation in measured variables between the two seasons, it is clear that the major differences were brought about by changes in food availability (Table 7.1).

The 1996/97 breeding season (good season) in contrast to the 1995/96 breeding season (poor season) was characterised by shorter duration of foraging trips and parents delivering a larger meal to their chicks. The period over which a parent remained with

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Chiaradia, A. 2001. Using penguins to help to save the fish. Turning the Tide 2: 19.

Chiaradia, A.. (2004). Pesca em tormenta – Como que as aves marinhas podem ajudar a salvar a pesca? [Troubled fishery – can penguins help to save the fish (and help themselves in the process)?] Gerenciamento Costeiro Integrado (Brazil). 3: 69 -70

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101 the chicks, the guard period, was longer but the period to raise a chick to its peak weight was one week shorter.

Differences for some variables during the course of each season were apparent as well. For instance, successful breeders undertook shorter incubation shifts, which equated to shorter foraging trips by the partner, and made more foraging trips than failed breeders. This was more pronounced in the bad season. The foraging trip duration was always shorter in successful breeders of both seasons. Chick growth was slower for all birds in a bad season.

This study involved two very different breeding seasons which have pointed to how variables related to breeding biology and feeding ecology respond to food supply (Table 7.1). This suggests that a monitoring program to provide detailed information for use in the conservation of the little penguin and its prey could be established by recording these and related variables each season for a number of years.

Although the little penguin is not threatened at present there is an unregulated fishery based upon several major prey items. These species are pilchard Sardinops sagax, anchovy Engraulis australis, red cod Pseudophycis bachus, barracouta Thyrsites atun, and warehou Seriolella brama. The overfishing of these species could compromise the penguins’ food supply in the future.

The variables measured in a monitoring program must have a predictable response, be easy to measure and above all be sensitive to change in the availability and quality of food within the foraging range. The most sensitive parameters for monitoring the availability of food to the little penguins appear in this study to be the foraging trip duration, during both incubation and chick rearing, and the meal size delivered to the chick. In the 1995/96 season, the trips duration increased for the whole colony from a particular date which indicated that the attendance pattern was changed due to

environmental conditions when food probably became less available. Chicks received 211 grams of food per day and chicks in a good breeding season received on average 35 grams more food than in a poor breeding season. These parameters integrate the effects of food availability over a very short time of perhaps 1 to 3 days and each trip is

therefore a snapshot of the food available together with the foraging ability of each parent penguin. Other parameters such as chick growth rate and fledging success integrate the effects of food availability over the whole breeding season. Data of onset of breeding may reflect effects of food availability during the non-breeding period when birds are able to forage widely (Table 7.1).

Breeding period Individual performance Intra-seasonal Inter-seasonal Integration period Factors which influence the variable

Before laying onset of breeding onset of breeding weeks, breeding season

Two weeks earlier for successful breeders

Incubation length of shifts length of shifts days, weeks

Shorter for successful breeders. Short, long, short throughout incubation.

number of foraging trips number of foraging trips breeding season

Successful breeders make more trips. Difference between successful and failed is more pronounced in a bad season.

foraging trip duration foraging trip duration

days, weeks, breeding season

Shorter for successful breeders. Short, long, short throughout incubation.

Guard length of guard length of guard

days, weeks, breeding season

Longer for successful breeders. Longer in a good season.

Post guard length of post guard

days, weeks, breeding

season Shorter in a good season.

foraging trip duration foraging trip duration foraging trip duration

days, weeks, breeding season

Shorter for successful breeders. Increases to the whole colony as season progresses. Shorter in a good season.

meal size meal size weeks

Larger for fledging chicks.

Decreases from the middle to the end of the season.

diet weeks

Successional changes in composition as the season progresses.

chick growth curve breeding season

Slower growth in a bad season than the growth in a good season. Reaches the asymptotic value one week earlier in a good season.

103 The response of a variable to food availability should be able to be separated from a response to other factors, both biological and environmental. One of the major constraints to a monitoring program is the ability to obtain data at appropriate intervals and with sufficient accuracy. In this study, data were obtained by daily observations of nest attendance and chick weight throughout two breeding seasons. Some reproductive variables like chick growth and chick fledging weight may be influenced by factors not related directly to food supply, such as breeding age and experience, and individual variation in growth rate. Foraging trip duration measured in days was shown to be different between the good and poor breeding seasons. However, if birds spend time at sea not foraging, foraging trip duration will reflect only feeding time but not necessarily food supply. This problem when investigating food availability was partially solved by examining several variables simultaneously in different stages of the breeding cycle. Automated data collection with the Automated Penguin Monitoring System, although not fully use in this study, can provide a very large body of high-grade data in the future. The above discussion was centred on understanding variations in little penguin breeding performance. However, a number of authors have suggested such studies also provide information on the stocks of commercial fish (eg CCAMLR 1982; Croxall et al. 1988; Furness and Barrett 1991b; Cairns 1992a; Furness et al. 1993; Montevecchi 1993; Crawford and Dyer 1995; Barrett and Krasnov 1996).

Although useful information might be obtained, such as the presence of fish of a particular species or year class, these results suggest that at present there are no clear signals reflected in the measured variables which would make the little penguin useful for providing quantitative data on specific fish stocks. Certainly variables related to foraging and breeding biology provide indirect information related to the prey (fish stocks) but such variables cannot be related directly to fish abundance in the absence of, as is now the case, independent assessment of fish stocks. The species composition of the diet of the little penguin during 1996/97 (the good breeding season for little penguin) contained virtually no anchovy or pilchard. Further the diet composition changed as the season progressed. Penguins preyed upon a temporal succession of red cod Pseudophycis bachus,

104 barracouta Thyrsites atun, warehou Seriolella brama and anchovy Engraulis australis. From this it may be inferred that pilchard and anchovy are not obligatory in the diet and that the little penguin is an opportunistic feeder. In addition, there is a size limit to the fish that little penguins are able to take and as some species of prey fish eg. barracouta, red cod and warehou grow they disappear from the penguin’s diet. The massive mortality of pilchards which occurred in Victorian waters in March 1995 may be one if not the principal cause of breeding failure of the little penguin in the following breeding season. However there appeared to be no carry over effect into the 1996/97 breeding season when breeding success of the little penguin was at its highest and pilchards formed no part of the diet. Defining the quantitative relationship between the little penguin and its prey may be possible in the future but only if fish stock surveys are conducted at the same time as land based studies on little penguin which forage in the same zone.

The little penguin population of Phillip Island consists of some 12000 to 14000 breeding pairs which may consume the equivalent of fish taken by the entire Victorian coastal fishery. During the breeding season the penguins are confined to a limited radius of 15 km (Weavers 1992) and there is an incomplete overlap between the penguin foraging range and the commercial fishery. Outside of the breeding season the penguins range widely with a possibly greater overlap.

The fact that little penguins and the commercial fishery take the same species makes it important that a fisheries management plan be developed which takes into account the food consumption of little penguins. Pilchards and anchovies have decreased

dramatically in importance in the penguin diet while the commercial catches of these fish have increased progressively. This potential competition between penguin feeding and commercial fishing has been noted previously [Hobday, 1992 #38] but it seems the implementation of measures to guarantee the future of both the food of the little penguin and a sustainable commercial fishery have been slow. The commercial fisheries are concentrated in Port Phillip Bay. There is no direct overlap between fisheries and the foraging range of Phillip Island penguins. However, there is evidence that Phillip Island region is a spawning area and contributes to the recruitment of pilchards and anchovies into Port Phillip Bay (Kailola et al. 1993; Collins et al. 1994; Hoedt et al. 1995). A

105 detrimental link between little penguin and pilchard/anchovy fisheries has not yet been established but waiting until over-exploitation is recognised by all parties could be proved inadequate. Ultimately it may not be possible to restore either the stock of commercially targeted fish or the depleted penguin population.

In the last 10 years, there has been a growing perception that it is not effective to base fisheries management policies only on single-species models. These target species models do not predict common events like large decadal shifts in species composition, abundance and productivity. Human-related activities such as overfishing are implicated in these fishing changes which increase pressure on top predators, like seabirds, and cause severe economic burden associated with declines in commercial fisheries. Fish population declines often lead to belated regulatory measures without a good

understanding of cause and effect (Lavigne 1992). It is desirable therefore, that fishery management takes a more holistic view of the ecosystem processes. Seabirds have evolved for millions of years as small sampling units which can integrate events over a long period of time so seabird data can be used to provide information on the availability of prey. The application of these ideas needs careful consideration since at best, the measure would be one to affect the availability of prey to predator rather than the absolute abundance of prey. Nevertheless, Cairns (1992a) postulated that there are several ways to use seabird data to refine fundamental indices on fishery models such as abundance, natural mortality and recruitment rates. Foraging trip duration of penguins combined with meal mass brought ashore to the chicks could be used to estimate abundance in the same way as the catch per unit effort of fisheries science. Data on provisioning rates and penguin diet composition can refine fish natural mortality rates since natural mortality is highly variable but a constant value is always assumed in fishery assessments. Prey fish will be in the penguin diet months or years before reaching the size to be commercially harvested so penguin prey are potential predictors of

subsequent recruitment to stocks of commercially harvested species. Fishery managers are now seeking to include ecosystem considerations into fishery management beyond the single species model. The differences in measured variables as response to

106 fluctuations of food supply indicate that little penguin data can be incorporated in a monitoring program as a potential indicator of food availability.